Add metrics regex docs (#3126)

* add metrics regex

Signed-off-by: yaron2 <schneider.yaron@live.com>

* Update daprdocs/content/en/operations/monitoring/metrics/metrics-overview.md

Co-authored-by: Hannah Hunter <94493363+hhunter-ms@users.noreply.github.com>
Signed-off-by: Yaron Schneider <schneider.yaron@live.com>

---------

Signed-off-by: yaron2 <schneider.yaron@live.com>
Signed-off-by: Yaron Schneider <schneider.yaron@live.com>
Co-authored-by: Hannah Hunter <94493363+hhunter-ms@users.noreply.github.com>

daprdocs/content/en/operations/monitoring/metrics/metrics-overview.md

@@ -72,6 +72,30 @@ spec:
     enabled: false
 ```
 
+## High cardinality metrics
+
+Depending on your use case, some metrics emitted by Dapr might contain values that have a high cardinality. This might cause increased memory usage for the Dapr process/container and incur expensive egress costs in certain cloud environments. To mitigate this issue, you can set regular expressions for every metric exposed by the Dapr sidecar. [See a list of all Dapr metrics](https://github.com/dapr/dapr/blob/master/docs/development/dapr-metrics.md).
+
+The following example shows how to apply a regular expression for the label `method` in the metric `dapr_runtime_service_invocation_req_sent_total`:
+
+```yaml
+apiVersion: dapr.io/v1alpha1
+kind: Configuration
+metadata:
+  name: daprConfig
+spec:
+  metric:
+      enabled: true
+      rules:
+      - name: dapr_runtime_service_invocation_req_sent_total
+        labels:
+        - name: method
+          regex:
+            "orders/": "orders/.+"
+```
+
+When this configuration is applied, a recorded metric with the `method` label of `orders/a746dhsk293972nz` will be replaced with `orders/`.
+
 ## References
 
 * [Howto: Run Prometheus locally]({{< ref prometheus.md >}})